Down draft carburetor



Jan. 12, 1932. H. w. LINKERT 1,840,727

' DOWN DRAFT CARBURETOR Filed July 11, 1929 2 Sheets-Sheet l .Z ZYEHEJ"I floward all in 6672:

Jan. 12, 1932. w. LINKERT DOWN DRAFT CARBURETOR Filed July 11, 1929 2Sheets-Sheet 2 W, m a Z w d W. W. H WW WI ll! HOWARD w. nmxanr,

Patented jan. 1-2, 1932 Her. v

or mnrarmroms,

INDIANA, Asstenon r 'rmi WHEELER- SCHEBLEB OABBURETOR COMPANY, OFINDIANAPOLIS, INDIANA, A'GORPOR ATION or INDIANA nm'r cmunmon.AppHcation-flled'iluly 11, 1929. Serial No. 877,855.

This invention relates to down draftl carburetors forinternal combustionengines and has special reference to a carburetor fed directly from afuel pump without the complication of a constant level fuel supplychamher with its attendant float operated mechanism.

It is one of the objects of this invention to provide a simple andimproved fuel supply arrangement for downdraft carburetors wherein theelimination ofthe usual float bowl precludes troubles from bowlflooding,

' which in the case of-a down draft carburetor would cause an overflowof fuel into the manifold and engine cylinders.

It is another object of this invention to pro 'vide a down draft airvalve carburetor without the customaryprimary venturi and air supplytherefor, controlling the entire air supply by means of an air valve.Such an arrangement permits an increase in the capacity of thecarburetor because even at low air flows a certain amount of vacuum canbe maintained by the air valve and its spring to promote breaking up ofthe metered fuel, especially with an air bleed into the fuel nozzle.This arrangement provides good idling and low speed operation while thehigh air flow capacity-of the carburetor is limited only by the throttlechamber because the venturi, mixture passageway and air valve size can.be made larger. The capacity can also be increased in a downdraftcarburetor because even with large air passageways no body loading ordeposition of liquid fuel can occur at low air velocities as would bethe case in an upright carburetor.

It is also an object of this invention to provide an air valvecarburetor without a primary venturi or air supply therefor and toincorporate a starting or choker control acting to increase the fuelmetering opening and to simultaneously lock the air valve against itsseat to facilitate starting, as by this arrangement all air will be shutoff except leakage about the valve and an air bleed to'the fuel nozzlewhile the fuel metering valve will be opened so that a plentiful supplyof fuel will be delivered.

It i a further object of this invention to provide an improved fuelsupply system for carburetors, embodying a fuel pump delivermgdirectly-to the carburetor fuel metering mechanism and of a capacitysuflicient to meet the maximum demands, the surplus fuel at partload oridling being returned to the suction side of the fuel pump or the'fueltank. Such an arrangement calls. for only a simple pump not limited towork under narrow pressure limits. In the case of a fuel return to thesuction side of the pump a simple float howl may be used which needsonly a small float and a large valve because the float does not have tohold against pressure. This makes the float bowl, float and mechanismsmaller and cheaper for large carburetors as compared to the usualcarburetor float chamber.

Other and further important objects of this invention will be apparentfrom the disclosures in the specification and accompanying to thecarburetor.

Figure 2 is a modified set-up embodying a fuel return to the suctionside of the fuel pump to eliminate a lon fuel return in the case of adistant fuel tan as when thetank is at the rearof a vehicle.

Figure 3 is a central section of a carburetor embodying the features ofthe invention.

Figure 4 is a section on the line IVIV of Figure 3.

Figure 5 Figure 3.

As shown on the drawings:

The carburetor of this invention will be referred to generally by thereference numeral 10 representing the body thereof. In Figures 1 and 2,fuel is supplied to the carburetor by a pipe 11 shown attached at theupper right corner thereof, and overflow fuel is conducted away from thecarburetor by a pipe 12 on the left side thereof. The

is a section on the line V-V of for installations where the fuel tank isclose.

main fuel supply tank 13 is shown in Figure 1 and a suction pipe 14extends from near the bottom thereof to the suction side of a fuel pum15 which discharges through the pipe 11. n this figure the overflow pipe12 discharges back into ,the main fuel tank.-

The fuel pump 15 referredto' is not shown in detail as a number of typesare commercially available, such as mechanically or electricallyoperated umps, for example. The fuel pump is not 1 narrow pressurelimits but is chosen of a capacity to deliver enough fuei for maximumengine speed and power, and may be steadily 0 erated at this capacitybecause of the overow, return pipe 12.

Figure 2 is a variation of Figure 1 in that the return pipe 12discharges into a float bowl chamber 16 having'a float 17 controlling anoutlet valve 18, the outlet 19 being Coupled into the suction pipe 14,just ahead of the fuel pump. This float mechanism is provided as asubstitute for a long return over flow pipe 12 in installations wherethe fuel tank 13 is at some distance from the carburetor. e floatmechanism serves to prevent the entrance of air into the suction line 14when only a small part of the fuel delivered by the pump actuallyoverflows into the return pipe 12, as occurs when the engine is operateclose to its maximum capacity range. The float mechanism also serves toreturn any excess fuel delivered into the float chamber back into thefuel line between the fuel pump and supply tank, thus acting as a returntrap between the carburetor and fuel supply tank. At low motor demand.the float mechanism returns most of the fuel pumped to the carburetorand at hi h motor demands returns very little, most 0 the pumped fuelbeing used by the motor. This float bowl can be made small, with a smallfloat but large float needle valve because the float does not need tohold the valve against pressure, so that the mechanism as a whole can bemade smaller and cheaper than the usual carburetor float bowl especiallyfor the large sizes of carburetors.

The carburetor body 10 is formed with a downwardly discharging mixingchamber 20, containing a verturi 21 and a throttle valve 22 on a shaft23, the bottom end or outlet of the passage 20 having a mounting flange24 for attachment to the manifold. The body 10 is provided with a topmember 25 containing a formed air valve seat 26 which opens i! 1 t o .achamber 27 communicating with the mlxing chamber 20. A disc air valve 28engages the seat and is normally held there against by being mounted ona rod 29 extending into a dash pot 30 and-having a piston 31 therein, aspring 32 being positioned between the pistonand the bottom of thedashot. The dashpot is formed imifl lel chamr 33 to which the outlet ordrain pipe 12 mated to work under is connected at a point high enough tomaintain the dash ot filled with liquid in order to damp out uttering ofthe air valve due to the suction impulses in the carburetor.

The pipe 11 from the fuel pump enters a passaged boss 34 on the topmember, the passage 35 in the boss opening into a threaded verticalpassage 36 containing a hollow shell 37 with ports 38 aligning with thepassage 35. The upper end ofythe shell 37 projects above the top memberand is closed by a head 39 bearing on a spring 40 which maintains theshell in its adjusted position. This shell forms the idling adjustmentin connection with fuel metering mechanism to be later described. Theports 38also align with a chamber 41 in the boss opposite the passage 35which chamber is connected by a pipe 42 with the fuel and dashpotchamber 33. This arrangement provides an overflow for fuel delivered bythe fuel pump which is in excess of that required by the engine. Thisoverflow relieves the-metering mechanism from undesirable variations ofpressure which would otherwise occur witha constant capacity fuel pump.

A fuel metering valve stem 43, has a tapered valve end 44 cooperativelyengaging a partial bottom closure 45 on the shell 37. The valve stem isguided in a depending boss 46 coaxial with the vertical passage 36, sothat when the valve stem is pushed upwardly to its limit it closes themetering orifice in the bottom 45 of the sleeve and. thus cuts off theflow of fuel. When opened to a greater or less extent fuel is permittedto flow from inside the shell 37 to the passage 36 below the bottom ofthe shell and is thence conducted by the passages 47 and 48, best shownin Figure 5, to a simple nozzle 49 projecting into the venturi 21- at aproximately the throat position thereof. opens into the passage 48 andserves to emulslfy the fuel discharged from the nozzle 49.

Adjustment of the shell 37 by means of its external head 39 shifts themetering orifice in the shell bottom 45 relative to the valve taper 44thus determining the initial or idling fuel supply for conditions whenthe air valve is closed.

As the rate of flow of air through the carburetor is changed, due to theopening of the air valve, the air and fuel must be kept inthe properproportions. This isaccomplished by linking the fuel metering valve tothe air valve. The air valve carries an arm 51 to which is pivoted oneend of a proportioning lever 52. This lever passes through and has aclosed sliding fit in a trunnion block 53 which is pivotally mounted ona movable fulcrum arm 54 on a shaft 55. The lever 52 passes to one sideof the fuel valve ide boss 46 and carries a fixed block 56 adacentthereto which has a connecting link 57 extending to the lower end of thevalve 11 air bleed aperture 50 v stem 43. Thus as the air valve movesdownwardly the proportioning lever 52 turns about the pivot of thetrunnion block 53 and gives to the valve stem 43 a motion that isproportional to thatof the air valve.

With the above described arrangement the opening of the fuel meteringvalve will be in direct proportion to that of the air adjustable bymeans of a lever to form the I normal range or economy settingvalve, astheoretically required by. the fundamental laws of an increase in fluidflow with an increase in the pressure dilferential within the carburetorwhich causes the air valve to open. Practically however it is usuallynecessary to vary the proportioning by altering either the taper-[of thefuel valve or the form of the air valve housing or seat. Further, anenriched mixture for full power at open throttle is desirable becausewith such an arrangement the carburetor may be adjusted for maximumeconomy at partial loads comprising the average driving conditions. Toprovide such an enriched mixture at open throttle. I provide an arm 58on the fulcrum shaft 55 which arm carries a screw 59 engageable by a cam60 on the throttle shaft when the; latter is in wide open position, thecam lifting the arm 58 and thus swinging the fulcrum arm 54 clockwise oraway from the fuel. and air valves, thus increasing the leverage of boththe air valve and the fuel valve, resulting in an increased openingmovement of the fuel valve relative to the air valve. From the geometryof Figure 3 it will be evident that this movement of the trunnion blockalso drops the fulcrum point to some extent, thusincreasing the fuelvalve opening relative to the air valve entirely aside from the changein the proportioning effect.

The fulcrum arm is held in its'initial position of maximum economy by aspring 61 acting against a lug 62 on the arm 54. This initial'positionis adjustable by means of a cam -63. which limits the counter-clockwisemovement of the fulcrum arm. This cam 63 is carried by a shaft 64 whichis externally A dash type of control is also. rovided facilitatestarting. This contro comprises a Bowden..wire 66, thetube 67 of .whichis.

- fastened at 68, while the wire is fastened to the end of a lever 69loose on the fulcrum shaft 55 but which engages a clamp yoke 70, whichis fastened to the shaft, when the lever 69 is pulled up by thedashcontrol. When this control is pulled up to its limit the fulcrum arm54 is shifted clockwise to its limit,

' as shownin dotted lines in Figure 3. Inthis -mary venturi is absentand when the a position the proportioninglever 52 is brought down hardagainst .theQtop edge '71'"of the wall ofthe air passage or mixingchamber 21 and thus locks the air valve shut, making starting very easybecause the customary privalve is locked against its seat all air willshut.

and the air bleed 50. The loose lever 69 is so arranged that thetrunnion block can be moved by the cam 63.or the-high speed cam 60without moving the dash ad ustment.

The operation of the various units meeting to form a complete carburetorhave been described in connection with the description of the structure,so that only a brief rsum of the operation is believed to be required.The fuel pump may be mechanically or electrically operatedfas umps ofeither type are commercially availa 1e and their structure form no partof the present invention. Fuel from the pump is admitted to the interiorof the sleeve 37 and the metering valve 45 controls the supply of fuelto the carburetor nozzle '49 in accordance with the air. valve openingas well as the modifying adjustments, Any excess fuel is discharged intothe overflow and 'dashpot chamber and from there is either returned tothe fuel tank or to the suction side of the pump. As the air valve opensin responseto increased suction in the carburetor, the fuel valve opens'proportionately thus decreasing the quantlty of fuel which flows intotheoverflow chamber and thence back to the tank or pump as the case maybe. 0

Itwill thus be seen that I have invented an improved and simplified downdraft carburetor which operates in a novel manner, takofl' except forminor leakage about the valve ing its fuel supply directly from a fuelpump without the interposition of a float controlled fuel chamber.

I am aware that numerous-details of con- 1. In a down draft carburetorthe combiv nation. of a downwardly discharging mixing chamber, a fuelvalve and a-nair valve'controlling respectivelythe quantities of fueland air delivered into said mixing chamber,

interconnecting 531d 'proportiomng means fuel and air valves so that thefuel valve is actuated by movements of the-air valve, a fuel dash potchamber having a dashpot iston therein linked to the air valve, auelpump for supplying'fuel directly.to the fuel valve, a reliefconnection for excess fuel leading from said fuel valveto the fuel dashpot;

and an overflow connection from said fuel dash pot to a source of fuelsupply forv said fuel pump.

2. In adown nation of a downwardly discharging mixing chamber,

a fuel valve and an air valve draft carburetor thecombih controllingrespectively the quantities of fuel and air delivered into said mixingchambfie ig proportioning means interconnecting. s fuel and air valvesso that the fuel valve is i point wherie said lever will be lockedagainst actuated by movements of the air means for varying the primitiveposition and the ratio of said proportioning means, a 'fuel dash potchamber having a dashpot piston therein linked to the air valve, a fuelpump for supplying fuel directly to the fuel valve, a relief connectionfor excess fuel leading from said fuel valve to the fuel dash pot, andan overflow connection from said fuel dash pot, to a source of. fuelsupply for said fuel pump.

3. In a down draft carburetor, a fuel valve and an air valve controllingrespectively the quantities of fuel and air admitted to the carburetor,a lever interconnecting the fuel and air valves so that the fuel valveis actuated by movements of the air valve, a movable fulcrum point forsaid lever for varying the movement of the fuel valve relative to thatof the air valve, and means for shifting said fulcrum point adapted inone position to lock the lever against movement whereby to preventopening of said air valve.

4. In a down draft carburetor, a fuel valve and an air valve controllingrespectively the quantities of fuel and air admitted to the carburetor.a lever interconnecting the fuel and air-valves so that the fuel valveis actuated by movements of the air valve, a movable fulcrum point forsaid lever for varying the movementof the fuel valve relative to that ofthe'air valve, means for shifting said fulcrum point adapted in oneposition to lock the lever against movement whereby to prevent openingof said air valve, and movable means for limiting the movement of saidshifting means in the opposite direction whereby, to define the economyposition of the fulcrum point. a

5. In a 'down draft carburetor, a fuel valve and an air valvecontrolling respectively the quantities of fuel and air admitted to the.ment to lock said air valve against opening.

In testimony whereof I have hereunto subscribed my name.

HOWARD W. LINKERT.

-carburetor,a lever interconnecting said two valves, a fulcrum for saidlever, and means for shifting said fulcrum on said lever to a pointwhere said lever will be locked against opening of said air valve.-

6. In a downdraft carburetor, a fuel valve and an air valve controllingrespectively the quantities of fuel and air admitted to the carburetor,a lever interconnecting said two valves, a fulcrum for said lever, andmeans for shifting said fulcrum on said lever to a op ng of. said airvalve, and means co-acting aidshifting means to define the maximumeconomy setting thereof.

7 'In a down draft carburetor, a fuel-=valve and an air va lvecontrolling respectively the quantities ofif uel and ai-r'gadmitted tothe carburetor, a lever interconnecting said two valves, a fulcrum forsaid lever, means for' shifting said fulcrum on said lever and meansvalve, adapted at one extreme of said fulcrum move

